java中数组怎么组合

<code class="java">public static void combine(int[] arr, int[] data, int start, int end, int index) {
    // 递归基线
    if (index == data.length) {
        // 打印组合
        System.out.println(Arrays.toString(data));
        return;
    }

    // 递归步骤
    for (int i = start; i <= end && end - i + 1 >= data.length - index; i++) {
        data[index] = arr[i];
        combine(arr, data, i + 1, end, index + 1);
    }
}</code>

<code class="java">public static void combine(int[] arr, int[] data, int n, int r) {
    int[] indices = new int[r]; // 索引数组
    while (true) {
        // 打印组合
        for (int i = 0; i < r; i++) {
            data[i] = arr[indices[i]];
        }
        System.out.println(Arrays.toString(data));

        // 找到下一个组合
        int i = r - 1;
        while (i >= 0 && indices[i] == n - r + i + 1) {
            i--;
        }
        if (i < 0) {
            break;
        }

        indices[i]++;
        for (int j = i + 1; j < r; j++) {
            indices[j] = indices[i] + j - i;
        }
    }
}</code>

<code class="java">int[] arr = {1, 2, 3, 4};
int[] data = new int[2];
combine(arr, data, 0, arr.length - 1, 0);</code>

<code>[1, 2]
[1, 3]
[1, 4]
[2, 3]
[2, 4]
[3, 4]</code>